Thermal insulation chemical composition and method of manufacture
FIELD OF THE INVENTION 
     The present invention relates to thermal insulation compositions and more particularly, but without limitation thereto, to a thermal insulation composition that is particularly useful in solid propellant gas generators that may be used in missiles control systems. 
     BACKGROUND OF THE INVENTION 
     Modern guided missiles need high performance solid propellant gas generators for providing high pressure and high temperature gases to the control nozzles of post boost control systems and the like. Prior art thermal insulations have not provided the high performance required for advanced weapon systems that must undergo severe operating requirements having long duration propellant burn requirements at very high pressures and temperatures. The primary requirements for thermal insulation of missile system high temperature solid propellant gas generators include high heat flow resistance; erosion resistance; producibility including bonding, layout, machining, dimensional control, mixing and calendaring; aging stability; system chemical compatibility; and non-toxicisity. In order to minimize toxic health hazards it has been necessary to use suitable non-toxic insulation materials in place of asbestos. Solutions to these and other requirements have been accomplished by the thermal insulation composition of the present invention. 
     OBJECTS OF THE INVENTION 
     An object of the present invention is to provide a thermal insulation composition that will have long shelf life and withstand severe high temperature and pressure conditions; 
     still another object of the present invention is to provide a cost effective, efficient and reliable thermal insulation composition; 
     a further object of the present invention is to provide a thermal insulation composition that is used in high temperature solid propellant gas generators that meets requirements relating to heat flow, erosion resistance, producibility, aging stability, system chemical compatibility and non-toxicity. 
     SUMMARY OF THE INVENTION 
     These and other objects have been demonstrated by the thermal insulation composition of the present invention which generally comprises an ethylene propylene, diene monomer (EPDM)/neoprene rubber binders containing silica powder filler and aramid fibers. The specific chemical constituents include: 
     BINDER 
     EPDM elastomer 
     2 Chlorobutadiene 1,3 elastomer 
     FILLER 
     Silica Hydrate 
     ANTIOXIDANTS 
     Polymerized Trimethyl Dihydroquinoline 
     Alkylated Diphenylamines and Diphenyl-p-Phenylendiamene 
     CURING AGENT 
     40% a,a&#39;Bis(Tert-Butylperoxy), Diisopropylbenzene 
     PROCESSING AIDS 
     Napthenic Process Oil 
     Synthetic Polyterpene Resin 
     FIBER 
     Aramid Fiber (0.25 inch) 
     ACTIVATOR 
     Zinc Oxide, Technical 
     All of the above described requirements have been achieved by the thermal insulation composition of the present invention which will be described in detail with reference to the accompanying tables. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The thermal insulation composition of the present invention generally comprises an ethylene propylene, diene monomer (EPDM)/neoprene rubber binder containing silica powder and aramid fibers. The specific chemical composition is set forth in Table I and the functional description of ingredients is set forth in Table II. 
     
                                           TABLE I                                 
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(Chemical Composition)                                                    
                        By Weight                                         
                        Composition in Parts per 100                      
                        Parts of Rubber Binder (PHR)                      
Function                                                                  
        Ingredient      Minimum                                           
                             Maximum                                      
                                   Nominal                                
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Binder  EPDM Elastomer  79.0 81.0  80.0                                   
        2 Chlorobutadiene                                                 
                        19.0 21.0  20.0                                   
        1,3 Elastomer                                                     
Filler  Silica Hydrate  29.0 31.0  30.0                                   
Antioxidants                                                              
        Polymerized Trimethyl                                             
                        1.9  2.1   2.0                                    
        Dihydroquinoline                                                  
        Alkylated Diphenylamines and                                      
                        0.9  1.1   1.0                                    
        Diphenyl-P-Phenylendiamene                                        
Curing Agent                                                              
        40% a,a&#39; Bis (Tert-Butylperoxy)                                   
                        5.5  5.7   5.6                                    
        Diisopropylbenzene                                                
Processing Aids                                                           
        Napthenic Process Oil                                             
                        4.9  5.1   5.0                                    
        Synthetic Polyterpene Resin                                       
                        4.9  5.1   5.0                                    
Fiber   Aramid Fiber (.25 inch)                                           
                        27.0 29.0  28.0                                   
Activator                                                                 
        Zinc Oxide, Technical                                             
                        4.9  5.1   5.0                                    
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                                           TABLE II                                
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(Functional Description of Ingredients)                                   
Ingredient      Description                                               
__________________________________________________________________________
EPDM Elastomer  EPDM elastomer; binder also adds chemical                 
                bond sites                                                
2 Chlorobutadiene 1,3 Elastomer                                           
                Chloroprene elastomer added to improve                    
                processing and bonding                                    
Silica Hydrate  Mineral filler to improve thermal                         
                properties (mixing and packing)                           
Polymerized Trimethyl                                                     
                Polymerized trimethylquinoline antioxidant                
                prevents aging degradation of the polymer                 
                chain                                                     
Alkylated Diphenylamines and                                              
                Diphenylamine; antioxidant used in combination            
Diphenyl-p-Phenylendiamene                                                
                with above for high temperature storage                   
                conditions                                                
40% a,a&#39; Bis (Tert-Butylperoxy),                                          
                40% active peroxide supported on Burgess                  
Diisopropylbenzene (curative)                                             
                KE clay; curative for both polymers also                  
                provides aging stability as compared to                   
                Sulfur, for example.                                      
Napthenic Process Oil                                                     
                Lubricating oil; improve mixing                           
Synthetic Polyterpene Resin                                               
                Tackifier added to improve green tack                     
                (adhesion between uncured layers)                         
Aramid Fiber (.25 inch)                                                   
                Aramid fiber reinforcement; improved char                 
                retention and thermal properties                          
Zinc Oxide      Activator for curing agent                                
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     The following are the process steps used to prepare the uncured thermal insulation composition of the present invention. 
     (1) The initial batch includes mixing the binders, antioxidants, processing aids and catalyst. A Banbury mixer is used for approximately 8 to 12 minutes (10 minutes optimum). 
     (2) The fiber filler is then mixed with the step (1) constituents. A Banbury mixer is used for three submixes each for approximately one minute. 
     (3) The curative is then mixed with the step (2) constituents. A Banbury mixer is used for approximately one minute to form a slab about 4 inches thick, one foot wide and from one to two feet long. 
     (4) The mixed slab of step (3) is then calendered to about 0.1 inch thick. 
     (5) The calendered material of step (4) is then remixed in a Banbury mixer for about one to two minutes to form a mixed slab as defined in step (3). 
     (6) The mixed slab of step (5) is then calendared to about an 0.1 inch thick sheet having an approximate 4 foot width. 
     (7) A thin plastic cover sheet is applied to one surface of the step (6) uncured insulation sheet and rolled for subsequent use. 
     (8) When used; the uncured insulation is cut to proper configuration; the configured insulation is laid up and the plastic sheet is removed. If additional insulation thickness is required another piece of uncured insulation is cut to proper configuration and laid up against the first uncured insulation sheet and the plastic sheet is removed. The first and second sheets are tacky and are pressed together to form contiguous insulation sheets. The process is repeated until the total desired uncured insulation thickness is achieved. 
     (9) The uncured insulation of step (8) is then cured by subjecting it to elevated temperatures wherein the time and temperature is dependent upon the total thickness of uncured insulation. 
     This invention has been described in detail with particular reference to a certain preferred embodiment, but it is to be understood that variations and modifications can be effected within the spirit and scope of the invention.